bind9 configuration file PROBLEM

I have a pc with debian 9 stretch and a router (Nano Pi r4s with openwrt) both with bind9. I have set the min-cache-ttl parameter of 80000 seconds on debian stretch, and when i try to set it also on the nano pi, it tells me that the maximum can reach 90 seconds !! How is it possible? How can I set a higher value ?? Thank you

debian 9 (/etc/bind/named.conf.options):

options {
        directory "/var/cache/bind";
        listen-on-v6 { none; };
        recursion yes;
        allow-transfer { none; };
        dump-file  "/var/cache/bind/cache.db";
        notify no;
        allow-notify { none; };
        forward only;

        forwarders {
                8.8.8.8;
        };

        //========================================================================
        // If BIND logs error messages about the root key being expired,
        // you will need to update your keys.  See https://www.isc.org/bind-keys
        //========================================================================
        dnssec-validation no;

        auth-nxdomain no;    # conform to RFC1035
        attach-cache yes;
        min-cache-ttl  86400;
        max-cache-ttl  87000;
        max-cache-size 1024M;
};

Nano PI R4S (/etc/bind/named.conf):

options {
        directory "/var/cache/bind";
        dump-file "/var/cache/bind/cache.db";
        listen-on-v6 { none; };
        recursion yes;
        allow-transfer { none; };
        notify no;
        allow-notify { none; };
        forward only;

        forwarders {
                8.8.8.8;
        };

        auth-nxdomain no;    # conform to RFC1035
        dnssec-validation no;
        attach-cache yes;
        min-cache-ttl  80000; ## ERROR! Max is 90!
        max-cache-ttl  43200;
        max-cache-size 1024M;
};